1. Field of the Invention
This invention relates to optical systems, more particularly for optical systems for high resolution display systems.
2. Background of the Invention
Spatial light modulator-based display systems have become more prevalent in recent years. Spatial light modulators in these systems typically comprise an array of individually addressable elements laid out in an x-y grid. They elements form the image by turning ON and OFF selectively based upon control signals. The elements control the perceived intensity of the image pixels by controlling the amount of light that reaches the final display surface.
These systems generate color images in several different ways. Sequential color systems typically use one modulator and sequence the color of light that illuminates the modulator. A separate image for red, green and blue, for example, is generated and the integration of the human eye blends those colors and their respective intensities for each pixel into a final image. Another approach is to provide three differently colored sources of light or three different modulators or modulator panels, each with color filters that produce the colored images for each color.
The three modulator systems have several different implementations. In some systems, a prism is used that splits a white light source into red, green and blue. The light travels out of the prism to the respective modulators, where it is modulated to create the image and then transmitted back into the prism for recombination and projection to the final display surface.
Several problems exist with these prisms. Surface reflections, absorption and scattering characteristics affect image quality. The latter two reduce the efficiency and quality of light. Additionally, light absorbed at some optical surfaces can induce thermal gradients in the optical glass, distorting the assembly. This can result in misconvergence. Further, for telecentric systems, the prism size must increase with the increase of the resolution and size of the device.
Therefore, a solution is needed for multiple spatial light modulator systems that provides color splitting without increasing the size of the optics, as well as reducing the absorption and scattering characteristics.